Enhanced implantable antenna method

ABSTRACT

As described herein vascular anchoring systems are used to position an implant in a vascular area such as a bifurcated vasculature with relatively high fluid flow, for instance, in an area of a pulmonary artery with associated left and right pulmonary arteries. Implementations include an anchoring trunk member having a first anchoring trunk section and a second anchoring trunk section. Further implementations include a first anchoring branch member extending from the anchoring trunk member. Still further implementations include a second anchoring branch member extending from the anchoring trunk member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to antennas for implantabledevices.

2. Description of the Related Art

Conventional implantable antennas can be constructed with a manner ofaccommodation with respect to incorporation into a body that is lessthan desirable. For instance, conventional antennas are found inenclosures, such as for heart pace makers, that require substantialroom, which may be overly restrictive for other applications, such asvascular implantation.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a sectional view of a first implementation of the enhancedimplantable antenna system using a tubular support structure.

FIG. 2 is a sectional view of a second implementation of the enhancedimplantable antenna system using the tubular support structure.

FIG. 3 is a sectional view of a third implementation of the enhancedimplantable antenna system using the tubular support structure.

FIG. 4 is a sectional view of a fourth implementation of the enhancedimplantable antenna system using the tubular support structure.

FIG. 4A is a sectional view of a conductive member as a solid conductor.

FIG. 4B is a sectional view of a conductive member as a bundle ofstranded conductors.

FIG. 4C is a sectional view of a stranded conductor as a solidconductor.

FIG. 4D is a sectional view of a stranded conductor as a coaxial set.

FIG. 4E is a sectional view of a conductor as a coaxial set.

FIG. 4F is a sectional view of a solid conductor and a stranded supportstructure as a coaxial set.

FIG. 4G is a sectional view of a conductor as a coaxial set.

FIG. 4H is a sectional view of a conductor as a coaxial set.

FIG. 5 is a sectional view of a fifth implementation of the enhancedimplantable antenna system using a backbone support structure with atriangular sectional shape.

FIG. 5A is a sectional view of a fifth implementation of the enhancedimplantable antenna system using a backbone support structure with acircular sectional shape.

FIG. 6 is a sectional view of a sixth implementation of the enhancedimplantable antenna system using at least the backbone supportstructure.

FIG. 7 is a side-elevational schematic of a first implant having aninductive H-field loop antenna in an uncompressed state using aspects ofan enhanced implantable antenna system and method and coupled to anelectronic enclosure.

FIG. 7A is a side-elevational schematic of the first implant having aninductive H-field loop antenna in a compressed state using aspects ofthe enhanced implantable antenna system and method and coupled to theelectronic enclosure.

FIG. 8 is a side-elevational schematic of a second implant in anuncompressed state having two of the inductive (H-field) loop antennasof FIG. 1 coupled to an electronic enclosure.

FIG. 8A is a side-elevational schematic of the second implant in acompressed state having two of the inductive (H-field) loop antennas ofFIG. 1 coupled to the electronic enclosure.

FIG. 9 is a side-elevational schematic of a third implant having two ofthe inductive (H-field) loop antennas of FIG. 1 in an uncompressed statecoupled to two electronic enclosures.

FIG. 9A is a side-elevational schematic of the third implant having twoof the inductive (H-field) loop antennas of FIG. 1 in a compressed statecoupled to two electronic enclosures.

FIG. 10 is a side-elevational schematic of a fourth implant in anuncompressed state having an electrical E-field antenna using aspects ofthe enhanced implantable antenna system and method and coupled to anelectronic enclosure.

FIG. 10A is a side-elevational schematic of the fourth implant in acompressed state having an electrical E-field antenna using aspects ofthe enhanced implantable antenna system and method and coupled to anelectronic enclosure.

FIG. 11 is a side-elevational schematic of a fifth implant having twoelectrical E-field antennas using aspects of the enhanced implantableantenna system and method and coupled to an electronic enclosure.

FIG. 11A is a side-elevational schematic of the fifth implant beinginserted into a tubular structure.

DETAILED DESCRIPTION OF THE INVENTION

As discussed herein, implementations of an enhanced implantable systemand method include use of one or more pseudoelastic and/or superelasticmaterials (referred to herein as “p/s elastic”) such as p/s elasticmetal alloys, such as Nitinol, and/or p/s elastic polymers to provide atleast a portion of the associated support structure for the implantableantenna. In implementations, the support structure has the general shapeof the associated antenna either by one or more portions as integratedsupport structures being directly incorporated into the antennastructure typically as a tubular support structure and/or portionsserving as a backbone support structure with a shape similar to thesupported antenna components such as including inductive (H-field) andE-field antenna implementations discussed herein.

Use of p/s elastic material in the antenna support structure providesgreater implantation adaptability and accommodation for the enhancedimplantable antenna compared with conventional approaches. The p/selastic materials used can have elastic response over large strains. Forinstance, when mechanically loaded, p/s elastic materials can deformreversibly even under strains, of up to approximately 6% to 10% so thatthe antenna structure will return to a desired shape after undergoinglarge strain levels. This large reversible elastic deformationcapability provides relatively high flexibility to accommodate minimallyinvasive insertion into the body, and other implantation scenarios.Furthermore, pseudoelastic materials exhibit a stress plateau at largerstrains, which is desirable for accommodating motion within the body andfor minimizing the stress on tissues. FIGS. 1 through 6 illustratevarious cross sectional views of antenna implementations that can beused with the implant versions shown in FIGS. 7 through 11.

A first implementation 100 of the enhanced implantable antenna systemincorporating tubular support is sectionally shown in FIG. 1 to includea coaxial set 102 of an electrically conductive core 104 filling atubular support structure 106, which is further encased by an externalelectrical insulator 108. Versions of the coaxial set 102 that use adrawn filled tube (DFT) wire of p/s elastic material, such as Nitinol,for the tubular support structure 106 can serve both a support role andan antenna role for the enhanced implantable antenna system. Given thevarious biological environments (such as in and around vicinities of theheart) of the enhanced implantable antenna system, the p/s elasticmaterial used for the tubular support structure 106 and other supportstructures discussed herein has long fatigue life (such as 1,000,000cycles, 10,000,0001 cycles, 100,000,000 cycles, and/or 400,000,000cycles for temperature ranges such as of at least between 33 degreesCelsius to 43 degrees Celsius or such as of at least between 0 degreesCelsius to 100 degrees Celsius)) to exist in areas such as inside of theheart.

Some versions of the enhanced implantable antenna system also use p/selastic materials with high elasticity: some having an elastic strainlevel of approximately 3% or more and others having an elastic strainlevel of approximately 6% or more for temperature ranges such as of atleast between 33 degrees Celsius to 43 degrees Celsius or such as of atleast between 0 degrees Celsius to 100 degrees Celsius to provideflexibility to be collapsed or compressed to allow for temporaryenclosure by delivery mechanisms, such as a catheter, a cannula, orother mechanical tubular structure of a delivery mechanism before beingreleased to expand into an uncompressed state to be located in avascular structure, other endoluminal tubular structure or biologicaltubular structure.

Since Nitinol is superelastic, it can be strained up to an elastic limitof about 6% without permanent deformation. Some P/S elastic materials,such as Nitinol, have an additional advantage in that they have shapememory properties, and can be “shape-set” to a desired geometry. In thecase of Nitinol, the shape setting process requires holding the wireformin a desired geometry while undergoing a heat treatment at a temperatureof approximately 500 degrees Celsius.

Due to the high shape-setting temperature, a Nitinol or Nitinol DFTantenna member requires shape setting prior to applying polymericelectrical insulation such as could be used for the external insulator108. Several different insulation techniques are possible, includingvapor deposition (e.g., Parylene), dip or spray coating (variouspolymers, either in the melt phase or prior to cross-linking), casting,injection molding, or by swelling a polymeric extrusion and sliding theshape-set wires into position. The latter technique is most easilyaccomplished using a silicone extrusion, which can be swelled in aliquid such as pentane, hexane, heptane, xylene, or a low molecularweight alcohol. The presence of the solvent in the silicone makes itparticularly lubricious, allowing insertion of the wires with minimalforce.

Like other p/s elastic materials, Nitinol and Nitinol DFT wires includeanother advantageous aspect. Nitinol has two crystalline states:martensite at low temperatures and austenite at higher temperatures. Thetransition temperature may be tailored by adjusting the metallurgicalcomposition and processing that the material undergoes duringmanufacturing, to produce transition temperatures at, above, or belowroom temperature. In medical applications, the transition temperaturecan thus be set between room temperature (˜20° C.) and body temperature(37° C.), so that a device transitions from its martensitic phase to itsaustenitic phase as it is introduced into the body. Only the austeniticphase is superelastic, whereas the martensitic phase is quite plastic.

In some implementations, p/s elastic material, such as Nitinol, can beprocessed as follows:

-   -   Shape-set the subject member, such as the coaxial set 102 and/or        the tubular support structure 106, to the desired shape at        approximately 500° C.    -   Cool the subject member to transition it into its martensitic        phase    -   Straighten (or otherwise shape) the subject member to facilitate        application of the insulating material, such as the external        insulator 108    -   Apply insulating material, such as the external insulator 108 to        the subject member    -   Implant final assembly steps can be completed with the subject        member in either phase as required by other considerations.

Electrical resistivities of materials of interest are summarized below:

Resistivity Material MicroOhm-cm Silver 1.629 Copper 1.724 Gold 2.44Aluminum 2.828 Iridium 5.29 Brass 7 Nickel 7.8 Iron 10 Platinum 10 Tin10.9 Steel 11.8 Lead 22 Nitinol SE 508 82 Titanium 55.4 MP35N 103.3 Ptlr25 NiTi/Cu 47.6

A second implementation 110 of the enhanced implantable antenna systemis sectionally shown in FIG. 2 to include two of the coaxial sets 102 ofthe conductive core 104 and the tubular support structure 106 bothencased in an external insulator 112.

A third implementation 114 of the enhanced implantable antenna system issectionally shown in FIG. 3 to include four of the coaxial sets 102 ofthe conductive core 104 and the tubular support structure 106 allencased in an external insulator 116. Any quantity of the coaxial set102 can be put together in this fashion.

A fourth implementation 120 of the enhanced implantable antenna systemis sectionally shown in FIG. 4 to include three of the coaxial sets 102of the conductive core 104 and the tubular support structure 106 andinsulated conductors 122 having an elongated conductive member 124encased by an insulator 126. The three coaxial sets 102 and the fourinsulated conductors 122 are further encased in an insulator 127. Thethree coaxial sets 102 and the four insulated conductors 122 are shownin a symmetrical configuration, but other symmetrical or asymmetricalconfigurations can also be implemented in various other numbers of thecoaxial sets and of the insulated conductors. Whereas otherimplementations can be made, given the implementation depicted in FIG.4, one to three of the coaxial sets 102 and one to four of the insulatedconductors 122 may be connected electrically in series or parallel toform an antenna configuration.

Each of the elongated conductive members 124 in some implementations aresolid conductors as the conductive core 104 as shown in FIG. 4A. Inother implementations, the elongated conductive members 124 are each abundle of stranded conductors 124 b such as shown in FIG. 4B. Each ofthe stranded conductors 124 b can be solid core conductors such assmaller diameter versions of the conductive core 104 as shown in FIG. 4Cor can be smaller diameter versions of the coaxial set 102 as shown inFIG. 4D or another type of drawn filled tube (DFT) wire or drawn brazedstrand (DBS) wire with a conductive core. To maintain superelasticproperties of the stranded wire, one or more of the strands would bechosen to contain Nitinol, either in solid, DFT, or other form.

In other implementations, each of the elongated conductive members 124can be versions of the coaxial set 102 as shown in FIG. 4E. Inalternative implementations, as shown in FIG. 4F, each of the elongatedconductive members 124 can be from a drawn brazed strand (DBS) 128 withstrands 128 a made from a fatigue-resistant alloy, and braze 128 b andcenter core 128 c made from a conductive material such as silver orother highly conductive material. Further implementations include theelongated conductive member 124 as a coaxial set 129, as shown in FIG.4G, with a tubular support structure 129 a (such as a DFT) made frommaterial other than the p/s elastic material (such as MP35N or otherfatigue resistant alloy). The tubular structure 128 a of the coaxial set128 can be filled with the conductive core 104. Other implementations ofthe stranded conductor 124 b can be made with versions of the coaxialset 129 as shown in FIG. 4H.

Since Nitinol and MP35N are far more resistive than either silver orcopper, in some implementations with portions of the tubular supportstructure 106 being made from Nitinol or the tubular support structure129 a made from MP35N and the conductive core 104 being made from ametal such as silver or copper, most of the electrical current will flowthrough the conductive core rather than the tubular support structure.Although highly fatigue-resistant composite wires such as MP35N DFT andDBS, when filled with a highly conductive metal such as silver, exhibitexcellent electrical conductivity, they do not exhibit the superelasticproperties or the shape memory properties of Nitinol.

Nitinol DFT, MP35N DFT, and DBS composite wires are commerciallyavailable with core cross-sections ranging from about 15% to 41% of thetotal area. Even with a 15% cross-section dedicated for the conductivecore 104, with many of the constructions, a majority of electricalcurrent would flow through a low resistivity conductive core, such asmade from silver, copper, or gold. In some applications, a material forthe conductive core 104 is chosen due to its enhanced radiopaqueproperties which result from the atomic number and mass density of thecore metal. For example, gold offers higher radiopacity than silver orcopper, while retaining relatively low resistivity.

A fifth implementation 130 of the enhanced implantable antenna system issectionally shown in FIG. 5 as having a backbone support structure 132including a p/s elastic core 134, encased in a sleeve 136. In someimplementations the p/s elastic core 134 is made from shape-set Nitinoland the sleeve 136 is made from a polymer such as PTFE, FEP, PFA, ETFE,PVDF, PEEK, LDPE, HDPE, polyurethane, silicone, or blends or alloys ofthese materials. The fifth implementation 130 further includes three ofthe insulated conductors 122 all of which are encased along with thebackbone support structure 132 in an electrical insulator 140.

Each of the three insulated conductors 122 each occupy a corner positionof a triangular configuration of the insulator 140 in one implementationas shown in FIG. 5, and has a circular sectional shape of the insulator140 in another implementation as shown in FIG. 5A. In someimplementations the backbone support structure 132 is used solely forstructural support to provide shape enhancement whereas in otherimplementations, in addition to structural support, the backbone supportstructure also provides antenna functionality. In both FIGS. 5 and 5A,the insulated conductors 122 are drawn as ellipses to illustrate thatthey can be helically wound around the backbone support structure 132.The form of the helix can range from zero to a plurality of turns perunit length, as required for a specific application.

A sixth implementation 150 of the enhanced implantable antenna system issectionally shown in FIG. 6 as having the backbone support structure 132surrounded by eight of the insulated conductors 122 and all encased inan insulator 152.

FIGS. 7-11 show representative versions of implants that incorporate theenhanced implantable antenna system including the implementationsdepicted above. In FIGS. 1-3 and 7-11, the implantable antenna systemmay be used for inbound power delivery to the implant, inbound signalcommunication to the implant, and/or outbound signal communication to anexternal system. In FIGS. 7-9, implants with versions of the implantableantenna system with inductive loop antennas are shown, which can haveone or multiple turns of any one of the implementations described above.

A first implant version 160 is shown in FIG. 7 to include an inductiveH-field loop antenna 162 coupled with an electronic enclosure 164 on afirst side 166 and a second side 168 of the electronic enclosure. Thefirst implant version 160 is shown in FIG. 7 as being in an uncompressedstate having a measurement of Zu along a first dimension and is shown inFIG. 7A as being in a compressed state having a measurement of Zc alongthe first dimension to be fitted into a delivery tubular structure 169having an interior 169 a with an internal diameter, D. In someimplementations, the ratio between Zu and Zc is at least 3:1 and inother implementations at least 5:1. The loop antenna 162 includes one ormore electrical conductors and one or more mechanical elements such asfound in the depicted implementations described above or with otherimplementations using aspects of the enhanced implantable antennasystem.

A second implant version 170 is shown in FIG. 8 to include two of theinductive (H-field) loop antennas 162 both coupled to an electronicenclosure 172 on a first side 174 and a second side 176. The secondimplant version 170 is shown in FIG. 8 as being in an uncompressed statehaving a measurement of Zu along a first dimension and is shown in FIG.8A as being in a compressed state having a measurement of Zc along thefirst dimension to be fitted into a delivery tubular structure 179having an interior 179 a with an internal diameter, D. In someimplementations, the ratio between Zu and Zc is at least 3:1 and inother implementations at least 5:1. The two loop antennas 162 provideadditional area for transmitting or receiving magnetic field signals,and they provide an alternate mechanical shape for anchoring the devicein an anatomic location. Having two of the loop antennas 162 to thesecond implant version 170 for inbound power, inbound communications, oroutbound communications provide added power and/or signal strength forinbound power or communication and added signal strength and/or fieldshaping for outbound communication. These loop antennas need not residein the same plane.

A third implant version 180 is shown in FIG. 9 to include a firstinductive (H-field) loop antenna 182 (having a first portion 182 a and asecond portion 182 b) and a second inductive (H-field) loop antenna 184having a first portion 184 a and a second portion 184 b) both coupled toa first electronic enclosure 186 (having a first side 186 a and a secondside 186 b) and a second electronic enclosure 188 (having a first side188 a and a second side 188 b). The third implant version 180 is shownin FIG. 9 as being in an uncompressed state having a measurement of Zualong a first dimension and is shown in FIG. 9A as being in a compressedstate having a measurement of Zc along the first dimension to be fittedinto a delivery tubular structure 189 having an interior 189 a with aninternal diameter, D. In some implementations, the ratio between Zu andZc is at least 3:1 and in other implementations at least 5:1.

The first portion 182 a of the first loop antenna 182 and the firstportion 184 a of the second loop antenna 184 both extend between thefirst side 186 a of the first electronic enclosure 186 and the firstside 188 a of the second electronic enclosure 188. The second portion182 b of the first loop antenna 182 and the second portion 184 b of thesecond loop antenna 184 both extend between the second side 186 b of thefirst electronic enclosure 186 and the second side 188 b of the secondelectronic enclosure 188.

The third implant version 180 has advantages associated with two loopantennas similar to the second implant version 170 and provides analternative shape for anchoring in an anatomic location. The thirdimplant version 180 also has the additional space for electroniccomponents associated with a second electronic enclosure, namely, thesecond electronic enclosure 188 spaced apart from the first electronicenclosure 186.

A fourth implant version 200 as shown in FIG. 10 has an electricalE-field antenna 202 coupled to an electronic enclosure 204. The E-fieldantenna 202 has an elongated member 206 coupled to the electronicenclosure 204 and extending therefrom. Coupled with the elongated member206 as also included with the E-field antenna 202, is a helical coilsection 208, which can be threaded into tissue to provide a mechanicalanchor for the fourth implant version 200.

The fourth implant version 200 is shown in FIG. 10 as being in anuncompressed state with the helical coil section 208 having ameasurement of Zu along a first dimension and is shown in FIG. 10A asbeing in a compressed state with the helical coil section having ameasurement of Zc along the first dimension to be fitted into thedelivery tubular structure 209 having an interior 209 a with an internaldiameter, D. In some implementations, the ratio between Zu and Zc is atleast 3:1 and in other implementations at least 5:1. The electronicenclosure 204 of the fourth implant version 200 can be either inelectrical or capacitive contact with surrounding tissue and would actas a local electrical ground reference. Given this arrangement, anE-field could be produced (for outbound signaling) or sensed (forinbound power delivery or signaling) between the electronic enclosure204 and the E-field antenna 202.

A fifth implant version 210 as shown in FIG. 11 has a first electricalE-field antenna 202 and a second electrical E-field antenna 204 bothcoupled to either end of an electronic enclosure 206. The first E-fieldantenna 202 and the second E-field antenna 204 are both configured asstraight sections which can be inserted into soft tissue to provide amechanical anchor. In the fifth implant version 210, the electronicenclosure 206 can be insulated from adjacent areas of tissue havingreceived implantation of the fifth implant version. An E-field could beproduced (for outbound signaling) or sensed (for inbound power deliveryor signaling) between the first E-field antenna 202 and the secondE-field antenna 204 as a dipole antenna. FIG. 11A shows the fifthimplant being inserted into a tubular structure 219.

From the foregoing it will be appreciated that, although specificembodiments of the invention have been described herein for purposes ofillustration, various modifications may be made without deviating fromthe spirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

The invention is claimed is:
 1. A method for manufacturing a flexibleimplantable antenna, including the steps: a. Selecting a superelasticmetal b. Selecting a second metal with higher electrical conductivitythan the superelastic metal c. Forming the superelastic metal into anH-field loop antenna d. Encapsulating the superelastic metal with thesecond metal having higher electrical conductivity wherein thesuperelastic antenna transitions from a martensitic phase to acompressible austenitic phase when implanted e. Electrically connectingthe second metal with higher electrical conductivity to at least onepoint of an electronic circuit f. Enclosing the electronic circuitwithin an implantable enclosure wherein a first end of the H-field loopantenna is coupled to the electronic circuit within the implantableenclosure and a second end of the H-field loop antenna is coupled to theelectronic circuit within the implantable enclosure.
 2. A method formanufacturing a flexible implantable antenna, including the steps: a.Selecting a first metal or metal alloy with two solid metallurgicalphases and a transition temperature b. Selecting a second metal withhigher electrical conductivity than the two-phase metal c. Forming thetwo-phase metal into a loop antenna by shape-setting it at a highertemperature d. Encapsulating the superelastic metal with the secondmetal having a higher electrical conductivity e. Electrically connectingthe metal with higher electrical conductivity to at least one point ofan electronic circuit f. Enclosing the electronic circuit within animplantable enclosure wherein a first end of the H-field loop antenna iscoupled to the electronic circuit within the implantable enclosure and asecond end of the H-field loop antenna is coupled to the electroniccircuit within the implantable enclosure.
 3. As in claim 2, where thetwo-phase metal is a nickel-titanium alloy.
 4. As in claim 2, where thetwo phases are austenite and martensite.